The present disclosure relates to an image reading device that performs document reading, an image forming apparatus incorporating such an image reading device, and a method for controlling an image reading device.
Image reading devices read documents. Some image reading devices include a light source in a moving body that moves in the sub-scanning direction. Moving the moving body causes a read line (a position at which light illuminates) to move. In a standby state in which no reading is performed, the moving body is kept on standby at a predetermined standby position. When document reading is started, the moving body is moved from the standby position to a position at which document reading is performed. As to such movement of the moving body, the following technologies are known.
Specifically, an image reading device is known that can perform reading by a first reading method whereby an image of a document which is being moved is read with an exposing device arranged in a first position and by a second reading method whereby an image of a document is read by making the exposing device scan the document at rest. The image reading device includes a motor for moving the exposing device over the movement range from the first position to the scanning region by the second reading method, an optical sensor which is arranged between the first position and a second position arranged within the movement range and which has a light emitting element and a light receiving element, a shielding member which is arranged in the exposing device and which shields light from the light emitting element, and a light transmission portion which is arranged in the shielding member and which transmits light from the light emitting element. The image reading device moves the exposing device arranged on the second position side of the optical sensor toward the first position by controlling the motor, and stops the movement of the exposing device based on a first output value of the optical sensor resulting from a first position-side end part of the shielding member reaching the optical path of the optical sensor and a second output value of the optical sensor resulting from the light transmission portion reaching the optical path.
In the image reading device, when no document reading is performed, the moving body is located at a standby position (home position). For example, after the main power is turned on until reading starts, the position of the moving body is located at the standby position. After completion of document reading, the moving body is returned to the standby position. Until subsequent document reading starts, the moving member is kept on standby at the standby position. When document reading starts, the moving body is moved from the standby position to a position at which document reading can be performed (reading start position). After the movement, reading starts.
A deviation in the position of the moving body from the standby position causes a deviation in the document reading position (reading start position). This may affect the image data acquired by reading. As one way to avoid that, when the moving body is located at the standby position, the stepping motor that moves the moving body can be magnetically excited. A holding torque then prevents a deviation in the position of the moving body, but leads to increased power consumption by the stepping motor during standby of the moving body.
On the other hand, to save power, it is alternatively possible not to magnetically excite stepping motor in the standby state. However, in a magnetically unexcited state, the rotor tends to move. The moving body moves when the image reading device is acted on by a force from the outside or is shook. This may cause a variation in the rotation angle of the stepping motor.
Conventionally, there has been a problem that, when the moving body is located at the standby position, the movement of the moving body (the variation in the rotation direction of the stepping motor) is not accurately or precisely detected. Thus, after a standby state with no magnetic excitation, phase adjustment is performed before the rotation is started. Phase adjustment is a process of attracting the magnet of the rotor by magnetically exciting the motor. Phase adjustment is performed with consideration given to the possibility of the stepping motor going out of synchronism due to a variation in the rotation angle of the stepping motor on standby.
On the other hand, in detecting movement on the order of one step (one line), the width of one line is very small (with 600 dpi, 42.3 μm). Thus, when detection relies on alternately transmitting and shielding light with a slit, it is difficult to provide the slit having such a width accurately.